1. Field of the Invention
The present invention relates to a sheet processing apparatus for receiving sheets, delivered from an image forming apparatus such as a copying apparatus, a printer, a facsimile apparatus or a composite apparatus, or from other office equipment, and stacking such sheets on a sheet stacking member, and an image forming apparatus incorporating or connected with the sheet processing apparatus, and more particularly to a technology for stably stacking sheets on a sheet stacking member.
2. Related Background Art
A sheet processing apparatus is already commercialized for receiving sheets delivered from an image forming apparatus such as a copying apparatus, a printer, or a facsimile apparatus and executing a sheet processing such as alignment, sorting, stacking, stapling, binding, punching or inspection. Also in certain types of the image forming apparatus, such sheet processing apparatus is incorporated or connected as an option for purchase.
A certain sheet processing apparatus is equipped, at an upstream side of a final stacking tray for stacking a sheet stack, with a process tray onto which sheets are delivered and stacked to form a sheet stack. The sheet stack is subjected to a processing such as a stapling on the processing stack member, and is then transferred from the process tray to the stacking tray and is stacked thereon.
In a sheet processing apparatus disclosed in Japanese Patent Application Laid-open No. H08-67400, a rear end impingement member is provided in an upstream side (rear end side of the conveyed sheet) on the process tray, and the sheets are driven at a lower surface thereof by a conveyor belt so as to impinge on the rear end impingement member, whereby the sheets are aligned in the conveying direction thereof.
In such sheet processing apparatus, a lateral end impingement member is provided at a side perpendicular to the conveying direction of the process tray (namely at a lateral side of the conveyed sheets) and the sheets are pushed by a pushing plate so as to impinge on the lateral end impingement member, whereby the sheets are aligned in the width direction thereof.